1. Field of the Invention
The invention relates to internal combustion engines of the fuel-injection type equipped with a catalytic exhaust converter and, more particularly in such engines, a system and a process for slaving the fuel-to-air ratio by a double feedback loop operating in real time.
2. Discussion of the Background
It is known how to use systems for modifying the quantity of fuel injected into an engine as a function of the exhaust-gas composition and, more particularly, of the oxygen content of these gases. To this end, the oxygen content is measured by means of a nonlinear sensor known as the "lambda" sensor or EGO sensor, where EGO is an English-language acronym for "Exhaust Gas Oxygen". Such a sensor is disposed upstream from the catalytic exhaust converter which treats the exhaust gases, and the signal delivered by this sensor is used to modify the quantity of fuel injected upstream from the engine cylinders via a first feedback loop.
In certain applications, it is known how to dispose a second lambda sensor downstream from the catalytic exhaust converter and to use the signal delivered by that sensor to measure, for example, the performances of the catalytic exhaust converter.
In other applications, the signal of this second sensor is used for slow regulation of the fuel-to-air ratio of the first loop by changing its operating point or by changing its transfer function. This slow regulation compensates for the aging of the first sensor on the basis of an average, but does not achieve real-time regulation of the fuel-to-air ratio, or in other words richness regulation, such that it is maintained at the stoichiometric value or close thereto, thus ensuring good operation of the catalytic converter and in turn less pollution.